304 
Nematoidea.- 
-ENTOZOA.- 
-Tkejiatoba. 
airangement upon tliat of Zeder. In the following- 
pages we shall adopt a somewhat similar method, and 
divide them also into five orders : — 
I* Nematoid, Round Worms — those which have 
a slender, elongated, cylindrical body, more or less 
filiform, and rigid or elastic The individuals have a 
true intestinal canal, and are of both sexes. 
II. Acanthotheca, Sheathed - hooked Worms — 
those which have a more or less club-shaped form, 
with a large head and the mouth in a depression of it, 
and surrounded with four strong, brown, simple hooks. 
The sexes are separate. 
III. Trematoda, Suctorial or Fluke Worms — those, 
the species of which have the bodygenerally flat, soft, and 
furnished with suctorial discs. They have no intestinal 
canal, and the sexes coexist in the same individual. 
TV. Acanthocepiiala, Hooked 
I Vorms — those in which the body 
is slender, round, subelastic, and 
provided at the anterior extremity 
or head with a retractile proboscis. 
They have no intestinal canal, 
but distinct genital organs, and 
distinct sexes. 
V. Cestoidea, Ribband or 
Band Worms — including the 
Cystic Worms or Hydatids 
( Cystica of Rudolphi) ; those 
that have an elongated, flattened, 
soft, continuous or jointed body, 
and a head either round and 
provided with a crown of small hooks, or flattened and 
furnished with two or four suctorial pits, called bothna. 
In these the two sexes are united in the same indi- 
vidual, and no trace of intestinal canal is to be seen. 
They multiply also by fissuration. 
Order I. — NEMATOIDEA [The Round Worms). 
This is the most highly organized order of all the 
Entozoa, and. contains a great many species. It com- 
prises also more species found inhabiting man, than an}^ 
of the other orders. They may be defined as worms 
with a filiform, or very long C3dindrical or fusiform body, 
covered with a resisting integument. The mouth is 
terminal or nearly so, and the vent is nearly terminal or 
preceding bj' a short distance a very slender tail. The 
intestine is straight. The sexes are separate. In size 
they vary much, some being scarcely a line long, others 
measuring an inch, and others again reaching the length 
of a foot. The greater proportion of them are found 
in the interior of the body of other animals, but a few 
are detected in the muscular system. 
The most typical genus of Nematoid or Round Worms 
is the genus Ascaris. The Ascarides are almost always 
found in the intestines of vertebrated animals ; and one 
species infests the alimentary canal of man. 
Order II.— ACANTHOTHECA. 
Thisorderhas been constituted to receive afewworms 
which Cuvier arranged amongst the Nematoidea, and 
Rudolphi amongst the Trematoda, but which differ from 
both these orders in several respects. The order maj' 
be defined as composed of worms having a straight 
intestine, with the mouth subterminal, and the vent 
terminal. The mouth is situated on the inferior sur- 
face, and is armed with two pairs of hooks, which are 
reti'actile into sheaths. They have a distinct nervous 
sj'stem, and the sexes appear to be separate. 
Genus Pentastoma. — This genus is almost the 
only one belonging to it. The species are never 
found in the intestines ; they are only to be found in 
the frontal sinuses, in the larynx or the lungs of Mam- 
malia and Reptiles, or in cysts or serous cavities. They 
are worms of an oblong or cylindrical shape, pleated 
transversely, or nearly ringed. The head is generally 
large, and the mouth is situated on the under surface, 
Fig. 207. 
with a longitudinal slit on each side, from which issue 
two pairs of simple or double hooks, retiactile into as 
many distinct cavities. The genus is represented by 
a figure of Pentastoma tcenioides. — See fig. 207. 
Order III.— TREMATODA. 
This is a very natural order of intestinal worms. They 
are more or less elongated, and of a depressed form, 
and provided with one or more organs of adhesion or 
suckers, by means of which they attach themselves to 
the various animals upon which they live as parasites. 
They are provided with a mouth and an intestine, but 
have no vent. The two sexes are united in the same 
individual. In those species which have been particu- 
larly watched the ova are elliptical, and the embryos 
when first hatched are generally covered with vibratile 
cilia, and undergo distinct metamorphoses in their pro- 
gress to maturity. ' The Trematodes are found in the 
various cavities of the body, in the tissue of certain 
organs, or even on the surface of the body ; and exist 
in both vertebrate and invertebrate animals. 
The various species which are found adhering to the 
external surface of the animals upon which they live, 
forming the families Onchobothriidce and Capsalidce, 
have, in consequence of their being outside parasites, 
been placed by several naturalists in the class Annelida 
Genus Distoma or Fluke-worms, the species of 
which are all found internallj’’, may be taken as the 
type of the family. The body of these worms is gene- 
rally depressed, sometimes of a cylindrical form, and is 
provided with two distinct and isolated suckers, one 
Pentastoma tsenioides. 
